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- Find each pipe's rate.
- Add filling rates and subtract emptying rates.
- Invert the net rate to get time.
Correct Answer: B
Correct Answer: B
Method / Topic: Pipes and Cisterns
The answer uses the net filling rate.
Short Explanation
Detailed Explanation
Correct Answer: B
Method / Topic: Pipes and Cisterns
<table cellspacing="0" style="border-collapse:collapse; height:20px; width:85px">
<tbody>
<tr>
<td style="background-color:#c0e6f5; border-bottom:1px solid #44b3e1; border-left:none; border-right:none; border-top:1px solid #44b3e1; height:20px; vertical-align:top; white-space:normal; width:85px"><span style="color:#000000">Net rate=1/15+1/10−1/30. Using denominator 30 gives 2/30+3/30−1/30=4/30=2/15 tank per hour. Time is the reciprocal, 15/2 hours, or 7.5 hours. The calculation is checked against the conditions in the
. A useful final check is to substitute the
s involving signs, denominators, amount versus interest, and distance versus speed.</span></td>
</tr>
</tbody>
</table>
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Learn + Solve: Shortcut, Trap & Fast Route Click to view shortcut, steps, and common mistake
Shortcut used, common trap, and the fastest solving route
- Find each pipe's rate.
- Add filling rates and subtract emptying rates.
- Invert the net rate to get time.
A pipe fills a tank in 15 hours and another fills it in 10 hours. A leak empties it in 30 hours. How long will the tank take to fill when all are open?
Explanation
Correct Answer: B
Method / Topic: Pipes and Cisterns
The answer uses the net filling rate.
Short Explanation
Detailed Explanation
Correct Answer: B
Method / Topic: Pipes and Cisterns
<table cellspacing="0" style="border-collapse:collapse; height:20px; width:85px">
<tbody>
<tr>
<td style="background-color:#c0e6f5; border-bottom:1px solid #44b3e1; border-left:none; border-right:none; border-top:1px solid #44b3e1; height:20px; vertical-align:top; white-space:normal; width:85px"><span style="color:#000000">Net rate=1/15+1/10−1/30. Using denominator 30 gives 2/30+3/30−1/30=4/30=2/15 tank per hour. Time is the reciprocal, 15/2 hours, or 7.5 hours. The calculation is checked against the conditions in the
. A useful final check is to substitute the
s involving signs, denominators, amount versus interest, and distance versus speed.</span></td>
</tr>
</tbody>
</table>
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